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Chapter 7 Usage of Various Functions
7-30
Relay response method.
• PID parameters are obtained by On/Off operation during 1 cycle of PV variation.
• PID parameters are obtained by amplitude and period of oscillation
• The On/Off operation will be occur at the SV value.
Process reaction curve method(PRC method).
• PID parameters are obtained by step response of process.
• It is useful fo r time 1
st
order time delay system expressed as following
1+
−
Ts
e
K
Ls
• Obtained parameters may not accurate if the process can’t approximated to 1
st
order system, In this
case, use relay response method.
SV
Period
Amplitude
MV
80% of SV
4000
Time delay(L)
63% of SV
Time constant(T)